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Air pollution may be causing infertility for a ‘significant number of couples’ a new study suggests.

Researchers looked at 6,500 men living in Taiwan and found that higher pollution was linked to poorer quality sperm.

The study showed that for every 5 ug/m3 increase in tiny particles called PM2.5s, there was a 26 per cent increased risk of being in the bottom 10 per cent of normal sperm size and shape.

The effect was found when particle counts rose over 25 ug/m3 . In London yesterday, particulates rose to 69 ug/m3 in some areas.

Although it is unclear how the pollution impacts sperm, researchers say that the components of fine particulate matter, such as heavy metals and polycyclic aromatic hydrocarbons, have been linked to sperm damage in experimental studies.

Free radical damage, brought on by exposure to air pollutants, may also damage DNA and alter cellular processes in the body, the researchers suggest.

“Although the effect estimates are small and the significance might be negligible in a clinical setting, this is an important public health challenge,” said Dr Xiang Qian Lao of the Chinese University of Hong Kong.

“Given the ubiquity of exposure to air pollution, a small effect size of PM2.5 on sperm normal morphology may result in a significant number of couples with infertility.”

Sperm counts in the west have plunged by 60 per cent in the past 40 years, with pesticides, hormone-disrupting chemicals, diet, stress, smoking and obesity all blamed for the decline. The new study suggests that pollution could also be driving infertility.

Higher pollution was linked to poorer quality sperm.

Lower sperm count is also linked to higher death rates, as well as to increased chances of suffering other diseases.

British experts were divided in whether pollution could trigger infertility, with some suggesting that other factors could be responsible.

Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said: “People who live in areas of high air pollution tend to be different from those in areas of low pollution in several ways.

“For instance, they may tend to work in different jobs, and there are several occupational factors that have been linked to fertility problems in previous studies.

“London and other big British cities do have some air pollution ‘hotspots’, but overall the level tends to be considerably lower than in Taiwanese cities.”

However Prof Allan Pacey, Professor of Andrology, at the University of Sheffield, said: “From this and other studies, I remain of the opinion that air pollution probably does have the potential to negatively influence male reproductive health.

“But the jury is still out about quite how and to what extent this impacts on male fertility, rather than measurable and small interesting changes in semen quality.”